In order to ascertain traffic density and to check on the reliability of various types of telecommunication equipment, such as meters serving for the determination of toll charges, it is known to utilize statistical counters which register such parameters as the number and the duration of attempted and completed calls taking place over a given trunk line as well as the number of metering pulses transmitted thereover. For a system-wide evaluation of such statistical data, the contents of these widely scattered statistical counters must be transmitted to a centralized location; this is generally done by periodically photographing the readings of the counters and feeding the data so ascertained to a central processor. The latter may compare these data with a statistical norm to detect, for example, temporal and local overloads or an excessive rate of unsuccessful engagements, i.e. calls that did not go through. By noting the origins of the calls for which toll charges are calculated with the aid of metering pulses, the processor may also help allocate the revenues from these toll calls among different companies sharing the system.
This mode of data collection is rather laborious and correspondingly expensive. The available information can be collated only infrequently, e.g. once per month, and is thus often outdated, complicating the back-tracing of any malfunctions at the time of evaluation. The correction of possible defects is delayed and the procedure itself often gives rise to error. Moreover, it is difficult to synchronize the collection of data over a wide area in order to obtain a comprehensive picture of operating conditions existing at a particular time.